Quantifying Precipitation Loss of Radiation Belt Electrons during Storm-time and Non-Storm-Time Dropouts

Relativistic electron flux in the radiation belt can drop by orders of magnitude within the timespan of a few hours. Studies of dropout events during geomagnetic storms are popular but relativistic electron flux dropouts are not always coupled to geomagnetic storms and can occur without the presence of one. In this study, we will be using a Drift-Diffusion model to simulate two contrasting radiation belt dropout events, both of which are GEM challenge events. The first event during 24 September 2013 is a non-storm time dropout event that has a Dst < -35nT and the electron flux dropout occurs across all energies. Unlike the first event, the second event during 01 June 2013 has a Dst < -140nT and an energy dependent dropout: electrons that are less than 700 keV saw an enhancement while MeV electrons saw strong depletion. We use the Drift-Diffusion model, which includes the effects of azimuthal drift and pitch angle diffusion, to quantify the electron precipitation loss for both of these events. By simulating the low-altitude electron distributions observed by 6 NOAA/POES satellites, we resolve the precipitation loss with both high spatial and temporal resolution and at a range of energies. The estimated pitch angle diffusion rates from the model are then compared with in situ wave measurements from Van Allen Probes to uncover the underlying wave-particle-interaction mechanisms that are responsible for the fast electron precipitation. Comparing the resolved precipitation loss with the observed electron dropouts at high altitudes, our results will suggest the relative role of electron precipitation loss and outward radial diffusion to the radiation belt dropouts during storm and non-storm times, in addition to its energy and L dependence.